Prostheses for replacement of joints commonly involve two parts having mutually articulating surfaces, and structure for mounting the parts to bone. To duplicate closely the structure and function of natural joints, the prostheses parts must be carefully shaped and sized, and must be properly oriented by the surgeon with respect to each other and with respect to the anatomy of the patient.
To achieve good surgical results, a surgeon should have as much freedom as possible during the surgical implantation procedure to vary the shape, size and orientation of prosthesis parts. Mainly for this reason, efforts have been made to provide prostheses that are modular in form so that various elements of a prosthesis can be individually selected and the prosthesis can be assembled and oriented according to the anatomical needs of the patient.
Modular prostheses for the hip joint are shown, for example, in Boleski et al., U.S. Pat No. 5,080,685, Gianezio et al., U.S. Pat. No. 4,520,511, Demane et al., U.S. Pat. No. 4,995,883, Luman, U.S. Pat. No. 5,002,578 and Rhenter et al., U.S. Pat. No. 4,693,724. Such prostheses for the most part involve a substantial number of parts that are held together in one configuration or another by means of mounting screws which operate to draw together tapered connections of the parts. Although some freedom of selection is provided by previous modular prostheses, the use of threaded mounting screws and tapered connections can lead to loosening of the parts and to other problems. Physical and chemical corrosion can become substantial problems due to weakening of the prosthesis and to biologic responses to corrosion debris and byproducts. See Jacobs, J. J. et al., Biological Activity of Particulate Chromium-Phosphate Corrosion Products, Collected Papers of the 21st Annual Meeting of the Society for Biomaterials, Mar. 18-22, 1995, p. 398, and Urban, Robert M., et al., Corrosion Products From Modular-Head Femoral Stems of Different Designs and Material Couples, Collected Papers of the 21st Annual Meeting of the Society for Biomaterials, Mar. 18-22, 1995, p. 326. Fretting corrosion caused by relative motion between adjoining surfaces leads to the production of debris which in turn may lead to accelerated wear between normally articulating joint parts of a prosthesis and to osteolysis. When gaps occur between adjacent surfaces of prosthesis parts, oxidation of the surfaces may lead to formation of an acidic environment and hence to chemical attack of the surfaces (commonly referred to as crevice corrosion).
It would be desirable to provide a modular prosthesis kit having elements that can be freely chosen and oriented by the surgeon in the operating arena and that can be strongly and firmly fastened to one another without the need for screw fasteners or tapered connections that are drawn together.